Overdiagnosis, and why more medicine is not always better

The idea that finding disease earlier is always better is intuitive, widely held, and true only when the disease would otherwise have caused harm.

What overdiagnosis is

The detection of a condition that would never have produced symptoms or caused death within the person's lifetime.

It is not a false positive — the abnormality is genuinely present.

It is not misdiagnosis.

The harm is that the person becomes a patient, receives treatment they did not need, and carries the label, the anxiety, the cost and the treatment risks for no benefit.

It cannot be identified in an individual, only in populations, which is why it is so difficult to communicate.

The clearest examples

Where the evidence is strongest.

Thyroid cancer, where diagnosis rates rose dramatically in several countries following increased imaging while mortality remained flat — a pattern that can only be explained by detecting disease that was never going to cause harm.

Some countries have since changed practice, with corresponding falls in diagnosis and no change in outcomes.

Prostate cancer, where PSA testing detects many cancers that would never have progressed, which is why active surveillance rather than immediate treatment has become standard for low-risk disease.

Breast screening, where overdiagnosis is quantified in programme information and is one reason informed choice material now presents both benefits and harms.

Incidental findings on imaging, where the great majority of unexpected abnormalities are benign and pursuing them produces net harm in many cases.

Why it happens

Several drivers.

Better technology detecting smaller abnormalities.

Widening disease definitions and lowering diagnostic thresholds, which converts previously healthy people into patients at the stroke of a committee.

Screening in low-risk populations, where the proportion of detected disease that is indolent is higher.

Incidental findings from imaging done for other reasons.

Defensive medicine.

Commercial incentives, including direct-to-consumer testing.

And the reasonable instinct of both clinicians and patients to look.

Why it is hard to see

The psychological trap.

A person whose indolent cancer is detected and treated experiences a good outcome and concludes that screening saved their life.

They cannot know that nothing would have happened without detection.

Which produces a population of grateful survivors who advocate for more testing, while the people harmed by unnecessary treatment are invisible even to themselves.

This asymmetry is why public enthusiasm for screening consistently exceeds what the evidence supports.

What good practice looks like

How the concept is applied.

Screening programmes are subject to formal appraisal against criteria including whether early treatment improves outcomes, rather than simply whether early detection is possible.

Programme information increasingly presents both benefits and harms in numbers.

Active surveillance rather than immediate treatment for low-risk cancers.

Guidance against routine imaging in the absence of indications.

Campaigns encouraging clinicians and patients to question tests and treatments that may not be needed.

And shared decision-making, where the person's own values determine the choice in genuinely balanced situations.

What to ask before a test

The questions that address this directly.

What is this test looking for?

What will change depending on the result?

What happens if I do nothing?

How likely is a false positive, and what would follow from one?

How likely is it to find something that does not need treating?

And what is the absolute benefit, expressed in numbers rather than percentages?

These are reasonable questions and most clinicians welcome them.

What this is not an argument for

Important to state.

It is not an argument against established screening programmes, which exist because they demonstrated mortality benefit in trials.

It is not an argument against investigating symptoms, where the pre-test probability is entirely different.

It is not an argument against vaccination, blood pressure control or any of the interventions with clear evidence.

It is an argument against untargeted testing in asymptomatic people, against commercial screening packages, and against the assumption that more information is automatically better.

The economics

Which follow from the clinical picture.

Overdiagnosis consumes resources — investigations, treatment, follow-up — that produce no health benefit and displace care that would.

For individuals in systems with charges, it produces bills for treatment that was not needed.

And it consumes the scarcest resource of all, which is clinical time that people with symptoms are waiting for.

Which makes appropriate restraint a form of care rather than a form of rationing.

General information only, not medical advice. Consult a qualified clinician about which tests are appropriate for you — and always seek assessment for symptoms.